In motor vehicles using hydrogen or using compressed natural gas (CNG) to power vehicle engines, present practice is that fuel is stored in on board tanks maintained at a maximum pressure in the range of about 5000 psi for hydrogen and 3600 psi for CNG. Higher pressures in the range of about 10,000 psi or more are anticipated as the use of hydrogen (for fuel cells) and hydrogen and CNG (for internal combustion engines) becomes more prevalent. The in situ techniques I have developed to the manage thermal energy differences between high pressure gas in a tank and the environment of the tank in a vehicle involve heat exchange devices fixed within the tank (to absorb and radiate heat) operatively interconnected with an external heat exchanger (correlatively to radiate and absorb heat) in the sequence of the refill and exhaustion of the high pressure gas within the tank. In the specification herein, high pressure hydrogen and high pressure CNG (compressed natural gas) are both referred to as a “gas” or “high pressure gas.” Both hydrogen and CNG are high pressure gases with which the invention is useful, typically, but not necessarily, in motor vehicle applications.
When the on board fuel tanks of a hydrogen powered vehicle are filled with hydrogen, the pressurized on board gas in the tanks may be characterized as having multiple forms of energy: 1) chemical energy associated with the hydrogen fuel itself (consumed in powering the vehicle), and 2) thermodynamic energy, namely, the mechanical, thermal and internal energy associated with the physics of high pressure refueling of a tank from sources of fuel at the high pressure gas refuel depot. Depletion of fuel from the tanks, although at a slower flow rate release the energy stored and thermally cools gas consumed during vehicle operation.